DE3343563A1 - Process for detection of dielectric breakdowns in an electrostatic precipitator - Google Patents

Abstract

The detection is by periodic sampling and evaluation of the pulsating precipitator DC voltage (u(t)). When there is a drop in voltage, the amount of the resulting relative precipitator DC voltage change (d(k)) over an evaluation time interval is compared with a computed permissible maximum amount (D(k)), and exceeding of this is used as the criterion of dielectric breakdown. <IMAGE>

Description

Method for detecting breakdowns in a

Electrostatic precipitator The invention relates to a method for detecting Breakdowns in an electrostatic precipitator that comes from an alternating voltage network via a Actuator, a high voltage transformer and a rectifier is fed and in the case of the breakdown detection, the filter DC voltage is periodically sampled where the sampling period is a fraction of the cycle duration of the pulsating DC filter voltage is selected and the relative change in DC voltage over de-inated evaluation tools and time segments is evaluated.

Since the efficiency (= dust separation efficiency) of an electrostatic precipitator is the electric field strength in the electrostatic precipitator9, on the one hand, a possible high field strength required 9 on the other hand, forms the breakdown limit (beginning Impact ionization of the gas molecules) an upper limit for the field strength, because a Breakdown short circuit (with failure of the filter effect) means therefore one leads the DC voltage applied to the electrostatic precipitator so that ideally at all times the breakthrough limit has just not been reached. However, this cannot be otherwise measured than to allow a breakthrough (at least to some extent) 0 Therefore In practice, the filter DC voltage is used - starting from a non-critical value - steadily increased until the breakthrough limit is reached, namely until a breakdown occurs. As soon as one is registered, the energy supply was interrupted to extinguish it, and a similar (not necessarily the same length) process follows. Main requirement of this The method is the rapid detection of breakdowns.

From EP-PS 0030320 there is a method for detecting breakdowns known, which has an incipient breakdown of a disproportionate filter voltage drop identified. The sampled values are derived from a half-wave of the electrostatic precipitator voltage compared with the sampled values associated with the phase of the previous half-wave.

Due to fluctuations in the mains frequency, the required is in-phase Assignment (synchronization) of the sampled values of successive filter voltage half-waves problematic. The object of the invention is therefore to develop a Breakdown detection method in which the effort for the evaluation of samples the electrostatic precipitator voltage is low.

According to the invention, this object is achieved by the following features: a) Each evaluation time segment corresponds to a sampling period; b) at a Filter DC voltage rise is a further evaluation of the scanned Refrain from values of the filter DC voltage; c) in the event of a drop the DC filter voltage becomes the amount of the relative DC filter voltage change compared with a computationally determined maximum allowable amount and its Exceeding used as a breakthrough criterion; d) the maximum amount allowed is dependent on the phase position of the sampled values within the cycle duration, determined from the duration of the sampling period and from the filter DC voltage further development of the claimed method is provided that the evaluation time segments consist of several, in particular two or three, consecutive sampling periods and that the evaluation device only then decides on breakdown detection, if more than two consecutive samples indicate a breakdown.

A further development of the claimed method consists in that also falling below a predetermined minimum value of the filter DC voltage is used as a breakthrough criterion.

In a further development of the claimed method, the relative change in the primary current peak values of successive half-waves detected and also the exceeding of a predetermined maximum value it this change used as a breakthrough criterion.

The main advantage of the invention is that the need a synchronization in the sense of an in-phase assignment of the sampled values there is no need for successive filter voltage cycles. The evaluation effort is thus considerably less than in Process according to EP-PS 0030320. In addition Compared to this method, the claimed new method requires a smaller one Number of storage locations for samples.

The training according to claim 2 increases the decision-making confidence of the procedure and minimizes the likelihood of false shutdowns.

The training according to claim 3 and 4 advantageously combine the new Acquisition method with the known absolute voltage or primary current criteria and include, in addition to increasing the detection security, a permanent mutual Monitoring of the evaluation bodies.

Based on an embodiment shown in the drawing the new method for detecting breakdowns in an electrostatic precipitator is described below described in more detail: Fig. 1 shows in schematic form an arrangement for implementation of the method, FIG. 2 shows an exemplary course of the pulsating electrostatic precipitator direct voltage.

An electrostatic precipitator 5 is fed from an alternating voltage network 1 via an actuator 2, a high-voltage transformer 7 and a rectifier 4. A sampler 6 periodically (sampling period T) records measured values of the filter DC voltage u (t) and transfers them to an evaluator 7, which determines an increase or decrease in the filter DC voltage from two consecutive samples Filter DC voltage to the breakdown limit is continuously continued. In the second case, evaluator 7 forms the amount of the relative DC filter voltage change d (k) according to the relationship where u (k) = u (kT) is the current sample and u (k-1) = u [(k-1) T is the previous sample. The variable d (k) is compared in the comparator 8 with a maximum permissible amount D (k) which the limit value transmitter 9 depends on the position of the current evaluation period within the cycle duration of the pulsating DC filter voltage, the duration of the sampling period and the DC filter voltage u (t), in that a sinusoidal curve (cf., for example, FIG. 2) is used as the basis for the oscillating component of the DC filter voltage.

Exceeds the amount of the relative DC filter voltage change the permissible maximum amount D (k), the breakthrough criterion is met, and the Energy supply of the electrostatic precipitator 5 is by means of actuator 2 for the duration and interrupted for the purpose of deleting the penetration. Is the amount of relative Filter DC voltage change d (k) does not exceed the permissible maximum amount D (k), the bringing of the filter DC voltage to the breakdown limit is continuously continued or maintain the reached level of the DC filter voltage 0 A containing all cases an exemplary curve of the pulsating DC filter voltage u (t) is shown in FIG. 2 shown. It is up to a breakthrough - to be detected at the voltage drop increased, which triggers an interruption in the energy supply0 thereby the filter DC voltage drops to the extinction voltage and remains at a low level Level up to a ^ fiMereinschalt the energy supply, the after a time safety interval takes place. The filter DC voltage u (t) becomes then systematically brought back to the breakthrough limit, etc.

The evaluation process described is not based on the qualitative recording of one punch.

Depending on the extent of the voltage drop on the electrostatic precipitator, you can also differentiate between high-current and low-current breakdowns. On low power Breakdowns (with a low voltage drop compared to the expected value) do not have to be an immediate shutdown of the energy supply necessarily take place because a Self-extinguishing can be expected.

To evaluate the sampled values, to determine the maximum allowable amount D (k) the relative filter DC voltage change d (k) and for outputting the control commands a process computer can also be used advantageously.

With regard to the maximum permissible amount D (k) of the relative filter DC voltage change For the special case, which is simple in terms of evaluation, d (k) is that the oscillating part the filter DC voltage is low as a percentage, the specification of a constant percentage D (k) = D sufficient.

4 claims 2 figures

Claims (4)

Claims 1. A method for detecting breakdowns in a Electrostatic precipitator, which consists of an alternating voltage network via an actuator, a high voltage transformer and a rectifier is fed and in which the breakdown detection Filter DC voltage is sampled periodically9 with the sampling period as a 3from part the cycle duration of the pulsating DC filter voltage is selected and the relative Filter DC voltage change evaluated over defined evaluation time periods the following features are given: a) Each evaluation = time segment corresponds to a sampling period (T) k b) with a filter DC voltage rise a more detailed evaluation of the sampled values of the filter DC voltage (u (t)) omit; c) if the DC filter voltage (u (t)) drops, the amount becomes the relative filter DC voltage change (d (k)) with a calculated permissible maximum amount (D (k)) compared and its exceeding as a breakthrough criterion used; d) the maximum allowable amount (D (k)) is dependent on the phase position of the sampled values within the cycle duration 9 from the duration of the sampling period (T) and determined from the DC filter voltage (u (t)). 2. The method according to claim 1 9 d a d u r c h g e -k e n n z e i c h n e t D that the evaluation time segments from several9 in particular two or three consecutive sampling periods (T) and that the evaluation device (7 - 9) only decides whether to detect a breakdown if more than two consecutive Samples show a DuhhßdEag. 5. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that also falling below a predetermined minimum value of the filter direct voltage (u (t)) is used as the breakdown criterion, 4. The method according to claim 1, 2 or 3, d a d u r c h e k e n n n z e i c h n e t that the relative change of the Primary current peak values of successive half-waves detected and also the exceeding a predetermined maximum value of this change is used as the breakdown criterion will.